1. Field of the Invention
The invention relates to a cooling system employing a heat exchanger with phase change material, and method of operation thereof, such as a heat exchanger that may be applied to a rear door of a server rack, and to a method of controlling the flow of coolant therein.
2. Description of the Background
Large computer server rooms include racks of servers that generate a great deal of heat. Further, as server capacity has grown, there has been a tendency to spread servers further apart so that the heat is easier to dissipate. This wastes floor space. Excess heat needs to be removed from such an environment, not only to ensure the proper functioning of the servers, but also to provide a comfortable working situation for employees.
Heat may be removed from such a server room by fans or by conventional air conditioning. However, it is not likely that existing building air conditioning would be sufficient, and air conditioning the entire room is a relatively inefficient way to remove the heat from the servers. If the air conditioning is increased to a level sufficient to cool the servers, the overall room temperature may be reduced even to a level where personnel may find it to be too cool. There is therefore a need for a way to cool the server racks directly, rather than the entire room.
One such device that is known in the art is the IBM eServer Rear Door Heat eXchanger, also known as the “Cool Blue® Rear Door”. This is a heat exchanger built into a four inch thick rear door adapted to fit a six foot 42U type rack, and includes a number of copper pipes through which water flows. Such a device is estimated to remove 55% of the heat from a fully populated server rack, or to be equivalent to an air conditioner with a capacity of 50,000 BTU.
A heat exchanger element 500 that may be used in the above device is shown in FIG. 5, and is made up of a single pipe, or sections of pipe joined together to form a single pipe, forming a flattened spiral coil 510.
Whilst the “Cool Blue® Rear Door” offers advantages over relying solely upon air conditioning, including reduced energy consumption and consequently reduced carbon emissions, it still leaves room for improvements that are the subject of this application.